A biomarker is a term used to refer to a biomolecule or cell that may be measured in the blood or tissue of an individual, and which concentration reflects the presence or severity of a disease state in the individual. Biomarkers may be specific cells, molecules, genes, gene products, proteins, enzymes, or hormones. Complex organ functions or general characteristic changes in biological structures may also serve as biomarkers. A biomarker may be used as an indicator of the biological or metabolic state of an organism. More specifically, changes in the amounts of a biomarker in an individual may be correlated with the progression of a disease in the individual, the risk of the individual to develop a disease, or the susceptibility of a disease in the individual to a given treatment.
Biomarkers have emerged as potentially important diagnostic tools for cancer and many other diseases. Continuing discoveries of such biomarkers and their aggregation into molecular signatures suggests that multiple biomarkers may be necessary to precisely define disease states. Parallel detection of biomarker arrays is thus essential for translation from benchtop discovery to clinical validation. Such a technique would enable rapid, point-of-care applications requiring immediate diagnosis from a physiological sample. Critically, such a system should also be capable of detecting very low levels of aberrant genes and proteins, as many biomarkers are present at minute concentrations during early disease phases (Etzioni et al., 2003, Nature Rev. Cancer 3:243-252; Liang & Chan, 2007, Clin. Chim. Acta 381:93-97; Fan et al., 2008, Nature Biotechnol. 26:1373-1378; Zheng et al., 2005, Nature Biotechnol. 23:1294-1301). Given these requirements, the use of conventional diagnostic assays has been a limiting factor (Fan et al., 2008, Nature Biotechnol. 26:1373-1378; Zheng et al., 2005, Nature Biotechnol. 23:1294-1301; Nagrath et al., 2007, Nature 450:1235-1239). An approach that is based on rapid, label-free sensing technologies would be ideally suited for clinical applications (Zheng et al., 2005, Nature Biotechnol. 23:1294-1301; Cui et al., 2001, Science 293:1289-1292; Jain, 2005, Clin. Chim. Acta 358:37-54; Burg et al., 2007, Nature 446:1066-1069; Kim et al., 2007, Appl. Phys. Lett. 91:103901; Stern et al., 2007, Nature 445:519-522; Stern et al., 2008, IEEE Trans. Electron. Dev. 55:3119-3130; Bunimovich et al., 2006, J. Am. Chem. Soc. 128:16323-16331).
Since their introduction in 2001, label-free nanosensors have demonstrated great potential to serve as point-of-care detectors capable of ultrasensitive, real-time, multiplexed detection of multiple biomolecular species (Zheng et al., 2005, Nature Biotechnol. 23:1294-1301; Cui et al., 2001, Science 293:1289-1292; Jain, 2005, Clin. Chin Acta 358:37-54; Burg et al., 2007, Nature 446:1066-1069; Kim et al., 2007, Appl. Phys. Lett. 91:103901; Stern et al., 2007, Nature 445:519-522; Stern et al., 2008, IEEE Trans. Electron. Dev. 55:3119-3130; Bunimovich et al., 2006, J. Am. Chem. Soc. 128:16323-16331). Despite their appeal, electronic nanosensors continue to be a challenge to implement, because fundamental limitations render them incapable of sensing molecules in complex, physiological solutions. Biofouling and non-specific binding readily degrade the minute active surface areas of such devices (<0.1 μm2; Gupta et al., 2006, Proc. Natl. Acad. Sci. USA 103:13362-13367). Furthermore, label-free sensing requires purified, precisely controlled buffers to enable measurements to be performed. In the case of nanowire field-effect transistor (FET) sensing, low salt (<˜1 mM) buffers are required to prevent screening of the charge-based electronic signal (Stern et al., 2008, IEEE Trans. Electron. Dev. 55:3119-3130; Stern et al., 2007, Nano Lett. 7:3405-3409). Because of these incompatibilities, label-free nanosensing has not been reported for complex, physiologic media, a critical step for translation of this technology to bedside applications.
There is thus a great need in identifying novel devices that may be used to purify biomarkers of interest before these biomarkers are analyzed by a nanosensor. These devices would allow the purification and concentration of biomarkers from biological samples, increasing the sensitivity of detection by the nanosensor and decreasing interference by the biofluid in which the biomarker is contained. The present invention fulfills this need.